Enhanced electrochemical performance of Li-rich cathode materials at high temperatures through fluorine and magnesium modification

Lithium-rich layered oxides represent a promising class of cathode materials for high-energy lithium-ion batteries. However, their application is hindered by suboptimal rate performance and cycling stability, particularly at elevated temperatures. This study focuses on enhancing the utility of lithium-rich cathodes in lithium-ion batteries by doping a 0.4Li₂MnO₃·0.6LiMn_1/3Ni_1/3Co_1/3O₂ composite with F and Mg. At ambient temperature (25 °C), the capacity retention after 200 cycles increased from 75.2% for the pristine cathode to 85.1% and 93.3% for the cathodes modified with F and Mg, respectively. At an elevated temperature of 55 °C, the pristine cathode exhibited marked capacity degradation, retaining only 61.6% after 100 cycles. In contrast, the F- and Mg-modified cathodes demonstrated enhanced durability, with capacity retentions of 81.8% and 85.6%, respectively. Moreover, voltage fading upon high-temperature cycling was mitigated, with the pristine cathode exhibiting a rapid decay rate of 1.97 mV per cycle, compared to the decay rates of 1.34 and 1.23 mV per cycle for the F- and Mg-modified samples over 50 cycles, respectively. For practical applications, the Mg-modified cathodes, which exhibited superior high-temperature performance, were assembled into solid-state batteries. These batteries demonstrated discharge capacities of 183 and 155 mAh g^–1 at 2–4.8 V and 2–4.5 V, respectively, when tested at 55 °C.